Any problem with sanding antifouling paint to smooth it?

Sep 15, 2016
617
Catalina 22 Minnesota
OK so I know this is an odd question but here is the deal. I have a boat with antifouling paint on it and this year it's not in the budget to remove it completely to redo the bottom (that's for the next year or so with VC performance epoxy). I trailer the boat 100% so I don't need the antifouling but as a quick help I was thinking about wet sanding it to 400 or 600 to try and smooth it out a bit (PO installed it like barn paint). I know it wouldn't be the prettiest but hey the paint has to come off eventually anyway. So anyone see a problem with this? Would it really help or am I just dreaming? Nationals are coming up and I'm hoping to do a little better than last time and will take any advantage I can get.
 
May 17, 2004
3,475
Beneteau Oceanis 37 LE Havre de Grace
Plenty of people (myself included) do just that between coats. I think you’ll find 400 is too fine to do any real smoothing if what’s there is rough. I’d make a pass with 80 grit to knock down the high spots, then wet sand 400 to polish a bit.

Definitely use serious PPE (respirator, etc) and a vacuum sander for any dry sanding.
 
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Likes: Justin_NSA
Feb 8, 2014
1,300
Columbia 36 Muskegon
Regular paint dust is bad enough, bottom paint is down right dangerous. On real thick nasty paint I have better luck with a Red Devil scraper. Not as much work as it sounds and the chunks coming off are too large to inhale. Sweeps up easier too. That's for total removal through.
 
Sep 15, 2016
617
Catalina 22 Minnesota
Thanks but remember I'm not looking to remove the paint completely with a scraper, just sand it down for better light air performance.

As for the safety I'm well aware of it as at one time I worked in a boatyard painting other peoples boats in Southern California when I was younger. My question is more in regards to are there any issues in having some more bare areas and some thicker so I achieve a smoother bottom and is it worth the performance advantage for the work.

When I finally get around to doing the bottom then I will strip all the paint, long board sand, fair, and recoat with epoxy (not antifouling).
 
Jun 8, 2004
2,563
Catalina 320 Dana Point
You can burnish a hard paint as you suggest, once had people on another boat remark that when heeled my bottom paint looked "shiney", like it was waxed. Have only done on fresh paint without a lot of built up old paint under it.
 
Oct 22, 2014
16,121
CAL 35 Cruiser moored EVERETT WA
LakeShark if you are only looking for smoothing, why not. You will find that the 400 will clog up quickly when used on antifouling paint. As soon as you scratch the surface of an ablative it will start to slough off into the sand paper. Clog up and then you got nothing. Doing it with 80 grit it does the same, but the coarseness if enough to throw a great portion of the created dust into the air.

I think I would try a medium grit abrasive pad. It would allow you to knock down the rough spots and not immediately clog up. When clogged you could rinse in water and clear up enough to try again.

The water would be contaminated and the PPE is essential.
 
Nov 6, 2006
9,225
Hunter 34 Mandeville Louisiana
Get some medium grit drywall mesh sandpaper and try that.. should smooth without clogging..
 
May 17, 2004
3,475
Beneteau Oceanis 37 LE Havre de Grace
My question is more in regards to are there any issues in having some more bare areas and some thicker so I achieve a smoother bottom and is it worth the performance advantage for the work.
No big problem. It still won’t be as smooth as if it were all done, but likely still better than what you’ve got now. I still don’t think 400 grit would do much at first and would still start with something more aggressive. If there are spots currently close to being bare be careful no to burn through or score any existing barrier coat or vinylester layer.
 
Sep 15, 2016
617
Catalina 22 Minnesota
Well the deed is done and the boat is sanded to a final wetsand finish of 800 grit (started with 220). She may not be as pretty but boy is she smoother. Water streams off the hull like wet paint now. First race is Saturday and it looks to be a drifter so well see if all that work helps.

Now onto my question since its still on my mind. Apparently the PO put standard abalitive over a harder bottom paint (i'm guessing VC-17 or something similar). I used 220 to sand off the abalitive but it barely touches the harder stuff underneath. Next year or so I wanted to completely strip the bottom and reapply something like VC performance epoxy don't need antifouling). My question is how do you get the hard stuff off? There is a barrier coat under most of it but it is as hard as a brick. Will a chemical stripper even touch it or am I in for a nightmare of sanding before I can fair and repaint?
 
May 17, 2004
3,475
Beneteau Oceanis 37 LE Havre de Grace
Certainly there’s plenty of sanding in your future. You should be able to start with a chemical stripper first and that should take a lot off. Whatever you need to sand I’d do with 60 or 80 grit. You could also look into media blasting, though that may thin the barrier coat and require some extra application.
 

RitSim

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Jan 29, 2018
247
Beneteau 411 Branford
I used Dumond Peel-Away. Did my hull over two seasons. It worked well but was on the expensive side after all was done. It didn't touch the barrier coat. There was an issue with retaining the paste and paper on near horizontal surfaces .
I might consider for a small boat but would not do agian on a bigger boat. It did easily remove 10+ layers of paint.
 
Sep 15, 2016
617
Catalina 22 Minnesota
@RitSim thanks for the link on the stripping chemicals. I may have to give that a shot. I'm not too worried about the barrier coat since i want to strip it all the way down and then fair the hull if i'm going to go to all the effort.

@Davidasailor26 I will certainly have to go coarser to get it all off i'm sure but unfortunately I don't know of anyone that could media blast it around me as we are a long way from a boat yard or major city.

Looks like unfortunately there is a lot of sanding in the years to come. Oh well for this season at least the boat is relatively smooth.
 

RitSim

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Jan 29, 2018
247
Beneteau 411 Branford
The paste stripper removed all 10 coats in one application if the paste and paper stayed on the hull. The only sanding was the paint residual. The left side showed the stripped hull and rhe rright was left for another year but you can see the paint flaking away
 

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Likes: LakeShark
Jan 1, 2006
6,089
Slickcraft 26 Greenport, NY
I don't think you have to remove the barrier coat to fair the hull and I would not do so. Since you'll likely be fairing with a thickened epoxy it will adhere to the epoxy barrier coat. After fairing you would possible cover the fairing with new barrier coat. Or un-thickened epoxy. That will save a S**t ton of sanding, probable rotator cuff injury and lifelong orthopedic problems. Barrier coat is hard and relatively thick if it was done right. You're not going to scare it by flashing some 60 grit sandpaper at it.
There is a book The Physics of Sailing, written by a physicist, which devotes a chapter to the notion of how smooth the bottom has to be. If you read it your shoulders will thank you.